My old gelding coliced a few months back.
He was on stall rest because the vet thought he was possibly foundering, and was taken off grain and just given as much hay as he wanted.
A week later, the vet came back out to x-ray him and the farrier was out to shoe him. He had to be sedated for all of that.
After all was said and done, we turned him out in a small paddock and he would walk a bit and then lay down. Everyone thought his feet were sore (his hooves weren't trimmed properly in years and he also had shoes put on). We (my fiance and I) went in there and comforted him, saying how much better he'll feel.
Well at 2am that next morning, we got a call from our BO saying that Gem was colicing and they already put a call into the vet.
He had a slight impaction.
The vet removed as much manure rectally as he could and then flushed him out (via his nose) as much as he could.
He did NOT oil him because at that point we were either going to admit him to a clinic (for surgery) or wait a few hours and see (he said he he oiled Gem, and he DID need surgery, when they would cut him open the oil would go in him abdomen and stuff)
We watched Gem until 5:30 that morning, He did not improve nor worsen. We got some sleep, picked up a treat for him (not to give, but to soak in water so he'd drink water) and we would also walk/trot him for 10 min and then 20 min rest. until he pooped. After hours of doing that, he finally pooped!
Even after his first poo, we kept walking/trotting him until he pooped some more.
He was kept for grain for a while longer, but he made a full recovery.
Colic is very scary, espeically to me as that was the first time I've ever witnessed anything like that.
We are not sure what caused it (we think a combination of the drugs, stress from moving to a new barn, being able to eat grass and then being on stall rest)
I know I didn't really answer any of your questions, but I thought I'd give you a story of what happened with me and my horse.